1. Field of the Invention
The present invention is in the field of radio and specifically relates to apparatus for simultaneously receiving a plurality of radio signals of widely differing strengths and for re-broadcasting the signals at an equal strength at the received frequencies or at shifted frequencies. In one embodiment, a locally-generated message may be broadcast on all of the channels simultaneously.
2. The Prior Art
One technique for re-broadcasting a plurality of signals is to use a receiver and transmitter dedicated to each signal channel. When the number of channels is large, this approach proves to be too expensive and the apparatus is too bulky. More seriously, this approach requires components that are highly stable in frequency.
A different approach is simply to apply the signals on the receiving antenna to a broadband amplifier, the output of which is connected to a transmitting antenna. This approach is rather naive for two reasons. First, to handle the same number of signals as the present invention, the broadband amplifier would need a power capacity of several kilowatts, which would be undesirable from the standpoint of size and cost. Second, in a real situation the signal strengths are usually quite diverse. A very weak station may be located in frequency quite close to a very strong station. To overcome this difficulty, earlier workers used tunable notch filters to attenuate the stronger signals. Unfortunately, the filters had to have an extremely high Q, so as to be able to attenuate a strong signal without at the same time attenuating a weak signal of a slightly different frequency. As a result of this high performance requirement, the filters tended to be difficult to adjust initially, and they had a tendency to drift.
These difficulties of earlier approaches have been overcome by the present invention.